Read the verse, starting in Exodus 20:4 >4 You shall not make for yourself a graven image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; 5 you shall not bow down to them or serve them; If you're worshipping a statue of Ganesh, that's idolatry. If you're bowing or praying to a statue of Mary, a cross, etc, that's idolatry. If you're serving something over God, such as "I should go church, but I decided to work overtime instead to make the payments on my luxury car"...you're serving that car instead of God and making an idol out of it. A good rule of thumb is that if you're creating an object and granting *that thing* religious significance or reverence, it's probably an idol. You serve the God of spirit and holiness, not sticks and stones and tangible objects. Additionally, crosses are very likely syncretism from the pagan cult of Tammuz to begin with. Jesus was crucified on a "stalos", which most closely translates to "stake". Sure, you *can* put a crossbeam on a stake if you really want to, but that's a stretch to begin with and sketchy given the obvious incentive to adopt pagan idols to bring in Tammuz devotees. Furthermore, when Jesus comes back, how do you expect Him to react to Christians wearing crosses? It'd be like JFK being resurrected to find his biggest fans wearing sniper rifle pendants or CIA badges. It's unbelievably creepy.